The present invention relates to a semiconductor laser coupling device for applying light to and receiving light from an optical fiber; and, more particularly, the invention relates to a semiconductor laser coupling device in which a light-receiving element, a laser element, and an optical fiber are aligned with each other on a substrate and are coupled to each other and are assembled in a case, to product an assembly which is suitable for outputting light to the outside, and to a method of mounting the assembly on a circuit board.
A conventional case of assembling a semiconductor element in an optical module is disclosed in Japanese Patent Laid-Open No. 152527/1997. The optical module described in this publication comprises an optical fiber, a substrate on which an optical element is mounted, a cap for fixing the optical fiber in position on the substrate, and a micro-capillary into which the optical fiber is inserted, the optical fiber being inserted into and fixed to the micro-capillary. A portion of the optical fiber having a length nearly equal to the micro-capillary is inserted into the micro-capillary to cause the tip end thereof to protrude from the tip end of the micro-capillary, and the protruding end of the optical fiber is arranged on a V-shaped groove on the substrate and is fixed thereto by the cap, whereby it is optically coupled to the optical element. The optical element and the optical fiber are then packaged by resin molding.
In the above-mentioned conventional optical module, the constituent parts for stable optical coupling of the optical module, that is, the substrate, the optical fiber, the micro-capillary, and the resin, which are constituent members of the optical module, are made of different kinds of materials and are coupled to each other. Therefore, when each member is subjected to a change in temperature, a thermal stress is produced in the members. That is, when the members made of different materials are expanded or constricted by a change in temperature, they are each subjected to a different amount of expansion or constriction, whereby they are bent. In the conventional optical module, no consideration is given to the fact that this bending deformation produces an optical axis deviation in the optical coupling of the optical element to the optical fiber.
Further, when an electric current is switched on the optical element to laser light, heat is produced at the same time. In some instances, depending on the structure or the material of the case, in particular, when using a resin case, the following problems are produced: heat dissipation takes a long time because the thermal conductivity of the resin is low, which increases the temperature of the semiconductor and reduces the optical output and produces a change in optical output and a change in lasing wavelength with a lapse of time.